What is the best .net programming language for artificial intelligence programming?
If you're talking about pure speed, C will get you there if you really know C and operating systems, etc. C++ is nicer in terms of user friendliness, and won't be much slower. I don't know much about VB but I don't see many benefits.

Please clarify at least generally what the AI program is about. It is extremely difficult to answer the generalized question "What programming language is best for AI"? if you know what I mean. (  I vote python :^]  )

To add: Any programming language of those listed is "stable" if you write things correctly, but C++ and its great IDE's will help you to that point much more nicely than C will. C, to fully utilize it's potential, requires much fiddling with delicate and precise systems. It'll go that little bit faster, as the cost of being less stable in the practical, " uh oh, now I need to troubleshoot this" sense.